ASoC: max98373: Add checks for devm_kcalloc

As the devm_kcalloc may return NULL pointer,
it should be better to check the return value
in order to avoid NULL poineter dereference.

Fixes: 349dd239

 ("ASoC: max98373: don't access volatile registers in bias level off")
Signed-off-by: Jiasheng Jiang <jiasheng@iscas.ac.cn>
Link: https://lore.kernel.org/r/20221116082508.17418-1-jiasheng@iscas.ac.cn
Signed-off-by: Mark Brown <broonie@kernel.org>